The Chinese
Not that the great wall was actually unmanned, but, you know. Not enough to actually stop anyone from getting through.
Genghis Khan just went around it
Interestingly the Great Wall of China allowed for control of immigration, emigration, taxation upon the silk road and kept raiding nomads outside. Most of the times the wall failed was because they failed to maintain it, complete it, or else garrisoned it with people who left the gates open purposefully or otherwise, or merely surrendered when Mongols came knocking or tried using Manchus when they came knocking. It also demonstrates how effective use of logistics and key geographical choke points is more effective than waaaaaaaaaaaaaaaaaaaaaaaaaall. Why couldn't the Chinese eradicate the northern nomads whilst maintaining military superiority? They simply could not extend their logistics to the deep northern interior, same way the French could not live off of the Russian land.
Though this is talking about walls from a military point of view and not a civil point of view, there are lessons to be learned. I am more fond of heavy-personnel with semi-permanent barriers, as fixed fortifications will be defeated eventually and are expensive to replace whilst semi-permanent are impossible to permanently circumvent because they can be replaced and change at will. As always, the biggest flaw to a wall is someone just opening the door. How did the Macedonian border fence fail? German activists let the migrants in :
D
Though then again, there are the Israeli walls, the Kurd trenches or the Morocco Wall are proof where you really can build a "fuck off" wall where the only way in is with a guard's permission or incompetence